Zero-Day Flaw in WordPress Plugin Used to Inject Malware into Sites

Cybercriminals have exploited a zero-day flaw in the popular FancyBox for WordPress plugin to inject malicious iframes into many websites. The vulnerability has been patched.

FancyBox for WordPress is a plugin that allows WordPress website administrators to integrate FancyBox, a tool used for displaying images, HTML content, and multimedia in a "lightbox" that floats on top of a web page. The plugin has been downloaded more than 600,000 times from the official WordPress website.

Numerous users started complaining earlier this week about having a malicious iframe from 203koko(dot)eu injected into their websites. All the compromised sites had been using the FancyBox for WordPress plugin.

While they haven’t disclosed the details of the vulnerability, researchers at the security firm Sucuri noted that the flaw allows an attacker to inject malware or scripts into vulnerable sites.

WordPress removed FancyBox for WordPress from its official repository until Jose Pardilla, the author of the plugin, released version 3.0.3 to address the issue. He later released version 3.0.4 to stop the malicious code from appearing on affected websites.

Sucuri has investigated the vulnerability in collaboration with Konstantin Kovshenin, who was credited by Pardilla for providing a fix for the bug, and Gennady Kovshenin. Gennady noted on Twitter that the vulnerability is persistent cross-site scripting (XSS).

Users are advised to update their installations as soon as possible.

Cybercriminals are increasingly targeting vulnerabilities in WordPress plugins to hijack websites. In December, Sucuri reported that attackers had compromised more than 100,000 WordPress sites by exploiting a flaw in the Slider Revolution plugin. In June, at least 50,000 websites had been hijacked by malicious actors who leveraged a vulnerability in the MailPoet plugin.